1. Field of the Invention
The present invention relates to a foreign particle inspection apparatus. More particularly, the invention relates to an apparatus used in production of semiconductor devices, which is suitable for inspecting for foreign particle on at least one of a surface of a protection film (as will be referred to a pellicle film) supported by a frame member and a surface of a photo mask provided with a pellicle film.
2. Related Background Art
FIG. 9 is a perspective view to schematically show a construction of a conventional foreign particle inspection apparatus of such a type.
In FIG. 9, a reticle 101, which is a substrate to be inspected is fixed on a carrier arm 105, and a pellicle frame 102 is mounted on a pattern formed plane of the reticle 101. A pellicle film 103 is extended on the pellicle frame 102 to cover the pattern formed plane of the reticle 101. Inspection light emitted from a light source 107 is obliquely incident onto the reticle 101 via an oscillation mirror 108, which is scanning means. A certain range is scanned with the inspection light in the x-direction on the surface of the reticle 101 through oscillation of the mirror 108.
An inspection area on the reticle 101 is constant in the conventional inspection systems of such a type. The reticle 101 is moved by the carrier arm 105 in the y-direction simultaneously with the x-directional scan in order to scan the entire surface in the constant inspection area. Scattering-diffraction light generated by the pattern formed surface of the reticle 101 is received by a photodetector 104, which conducts a photoelectric conversion of the received light. A foreign particle is detected based on an output signal of the photodetector 104.
The inspection area in the conventional foreign particle inspection apparatus is next explained with reference to FIG. 10. FIG. 10 shows a condition in which the reticle 101 has been moved by the carrier arm (not shown) in the y-direction to move an inspection position from an inspection start position 106a on the reticle 101 (a point where the inspection light is first incident onto the reticle 101 without being interrupted by the pellicle frame 102) leftward to an inspection position 106b closer to an internal wall 102a on the left side of the pellicle frame 102. In FIG. 10, a solid line represents inspection light (incident light) incident from the light source (not shown) onto the reticle 101, and an alternate long and short dash line represents inspection light (receiving light) directing from the surface of the reticle 101 to the photodetector 104. Further, I.sub.1 represents a direction of incident light at the inspection start position 106a, and I.sub.2 a direction of incident light at the inspection position 106b.
As an incident angle .alpha. (an angle of incident light relative to a normal line to the reticle 101) and an light receiving angle .beta. (an angle of receiving light relative to a normal line to the reticle 101) increase, any pellicle film 103 generally decreases its transmittance. If the transmittance of the pellicle film 103 is not 100% for at least one of the incident angle .alpha. and the light receiving angle .beta., the incident light and the receiving light repeat reflection between the pellicle film 103 and the surface of the reticle 101.
Consider such a case that the internal wall 102a of the pellicle frame 102 is at an intersection 109a, 109b of optical paths of the incident light and the receiving light. The frame internal wall 102a is indirectly illuminated by the incident light I.sub.2 to generate scattered light in such a case. The scattered light from the internal wall 102a exits on the optical path of the receiving light, so that it is received as stray light by the photodetector 104, which will be referred to as frame stray light.
The conventional foreign particle inspection apparatus is structured such that the incident angle .alpha. and the receiving angle .beta. are set small enough to reduce an amount of frame stray light, whereby the amount of stray light can be ignored in the inspection area A (FIG. 10) for any pellicle film.
There is, however, such a relation between either the incident angle .alpha. or the receiving angle .beta. as described and the foreign particle inspection capability that an intensity of scattered light from a foreign particle increases as the incident angle .alpha. or the receiving angle .beta. becomes larger, thereby to enhance the foreign particle inspection capability. In the conventional foreign particle inspection apparatus, if an inspection object is a pellicle film or a photo mask with a pellicle film, a location arrangement for radiating means and light receiving means of inspection light would be extremely restricted, whereby the inspection precision cannot be improved. Also, since the inspection area is always constant in the conventional system, there is such a problem that an area close to the frame internal wall cannot be inspected even in case of using a pellicle film and/or a pellicle frame which are relatively unlikely to cause scattered light.